Leases - (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) ft²	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018
Lease terms
Option to extend			20
Weighted-average remaining lease term	9 years		9 years		10 years
Weighted average discount rate - Operating leases	4.90%		4.90%		4.90%
Increase in Right-of-Use Asset	$ 1,000		$ 1,035	$ 114,989
Increase in operating lease liability	1,000
Lease expense
Operating lease expense	6,868	$ 6,144	19,662	16,789
Variable lease expense	1,463	1,185	4,090	3,487
Rent expense	$ 8,331	$ 7,329	$ 23,752	$ 20,276
Minimum
Lease terms
Remaining lease terms	1 year		1 year
Maximum
Lease terms
Remaining lease terms	10 years		10 years
DE1 Denver CO [Member]
Lease terms
Net Leased Space | ft²	5,300